The present invention relates to a transparent resin utilizable as an elementary material of plastic lens, a process for production of said resin, a plastic lens, and a casting composition for production of the transparent resin.
As a material of optical lenses, resins of high transparency such as acrylic resin, diethylene glycol bis-allylcarbonate resin (for example, CR-39), polystyrene, polycarbonate and the like have hitherto been used. Of these resins, diethylene glycol bis-allylcarbonate resin which is a thermosetting resin is most extensively used as a material of eyeglass lens. This is due to the high transparency, low dispersibility (high Abbe number) and excellence in heat and impact resistances.
However, a lens made of diethylene glycol bis-allylcarbonate is disadvantageous in that its refractive index is as low as 1.50 and its thickness is unavoidably greater than that of a lens made of glass (this tendency becomes more marked as thickness of lens increases). Further, this type of lens is inferior in abrasion resistance, like general plastic lenses. Although a method of coating the surface of this type of lens with an organosilane type hard coat film has been proposed in order to overcome this disadvantage, an untreated plastic lens is insufficient in adhesive strength to the organosilane type hard coat film and cannot make a uniform adhesion. In other words, the organosilane type hard coat can be formed only after treating the surface of plastic lens.
Further, it is an increasing demand of the time to reduce the weight of eyeglass, so that material of low specific gravity for production of eyeglass is actively being studied. For example, Japanese Patent Unexamined Publication No. (JP-A) 2-238006 has proposed acrylic resins using 2,2-dialkyl-1,3-propane-di(meth)acrylate. This material, however, is unsatisfactory because its specific gravity is so high as about 1.31 to 1.35 and this material is inferior in dyeability and adhesiveness to organosilane type hard coat film. In JP-A-5-215903, there has been proposed a copolymer constituted of [di(meth)acrylate having straight chain alkyl group as spacer]/[(meth)acrylate having alkyl group]/aromatic vinyl compound/other monomer. Although this material has a low specific gravity, it is readily deformable in the process of dyeing and hard coating due to its low heat resistant temperature. Further, all the materials mentioned above are insufficient in strength so that they are readily breakable in the course of boring process.
JP-A-4-126710 has proposed a copolymer constituted of [alkylene oxide group-containing bifunctional (meth)acrylate]/[aromatic vinyl monomer]/[polymerizable monomer or polymerizable oligomer having a polymerizable double bond and a molecular weight of 98 or above]. However, this material is yet insufficient in the lowness of specific gravity and its hue tends to become yellowish.
Further, as resins improved in the adhesive property to hard coat film, a copolymer constituted of [aromatic ring-containing di(meth)acrylate]/[aromatic ring-containing monomer]/[hydroxyl group-containing monomer] (JP-A-58-76410) and a copolymer constituted of [aromatic ring-containing di(meth)acrylate]/[aromatic ring-containing monomer]/[epoxy group-containing monomer] (JP-A-58-89606) have been proposed. These materials, however, are yet unsatisfactory in the adhesive property to organosilane type hard coat film, even though adhesion to glass film after glass vapor deposition is improved. Further, the latter resin is undesirable from the viewpoint of moldability because its adhesiveness to glass mold used in cast polymerization process excessively increases as the proportion of epoxy group-containing monomer in the copolymer increases.
As has been mentioned above, there has hitherto been disclosed no plastic lens nor resin for plastic lens which is excellent in hue and well-balanced between strength at the time of boring processing and specific gravity, has the properties required of a plastic lens, and can directly be coated with an organosilane type hard coat film without surface treatment.